Due to an emphasis on operability and from the perspective of environmental friendliness, scanning electron microscopes with a specific focus on size reduction have been under development in recent years. Accordingly, there is a need to reduce the sizes of the condenser lenses provided in the column. In general, in order to reduce the size of an electromagnetic coil-type condenser lens, either the number of turns of the coil wire or the coil wire diameter has to be reduced.
If the number of turns were to be reduced with the coil wire diameter left unchanged, although the electromagnetic coil would naturally become smaller, the magnetic field strength would decrease. On the other hand, if the coil wire diameter were to be reduced with the number of turns left unchanged, although it would be possible to achieve a size reduction while maintaining the magnetic field strength, the resistance of the coil wire would increase, causing an increase in the amount of heat generated. Unless the magnetic field strength is maintained, the spot size of the electron beam with which the sample is irradiated cannot be made small, and the resolution of the scanning electron microscope cannot be maintained. In addition, if the column surface temperature were to rise due to an increase in the amount of heat generated, it would no longer be possible to meet various standards, such as IEC, etc. In terms of performance, image shifts, and focus offsets would occur due to temperature drift. Therefore, in order to reduce the size of an electromagnetic coil-type condenser lens, it is necessary to solve such problems as the decrease in magnetic field strength, and the increase in the amount of heat generated.
In order to solve such problems, by way of example, Patent Document 1 discloses a structure where, instead of electromagnetic coil-type condenser lenses, permanent magnet coil-type condenser lenses that are smaller than those of an electromagnetic coil-type are adopted.